Immigration law concerns both first-order issues about the number and types of immigrants who should be admitted into a country and second-order design issues concerning the legal rules and institutions that are used to implement those first-order policy goals. The literature has focused on the first set of issues and largely neglected the second. In fact, many current controversies concern the design issues. This Article addresses the second-order dimension and argues that a central design choice all states face is whether to evaluate potential immigrants on the basis of pre-entry characteristics (the ex ante approach) or post-entry conduct (the ex post approach). The ex post system provides more information and thus results in more accurate screening than does the ex ante system, but it also may deter risk-averse applicants from making country-specific investments that benefit the host country. Focusing on this important tradeoff for states, as well as other costs and benefits of the two screening regimes, this Article evaluates America\u27s reliance on an illegal immigration system, the growth in ex post screening during the twentieth century, and America\u27s unique focus on family-related immigration
